Generation of the precursor (lyso-PAF) of platelet-activating factor via a CoA-dependent transacylase.

The microsomal fraction from rat spleen was shown to possess a CoA-dependent transacylase activity that produced 1-[3H]alkyl-2-lyso-sn-glycero-3-phosphocholine ([3H]lyso-PAF), the immediate precursor of PAF in the remodeling pathway of biosynthesis, from 1-[3H]alkyl-2-acyl-sn-glycero-3-phosphocholine. This CoA-dependent transacylase did not require ATP or metal ions for activity making it unlikely that either acyl-CoA-synthetase or a Ca(2+)-dependent phospholipase A2 were involved in the generation of [3H]lyso-PAF. Albumin, in addition to CoA, was required to demonstrate the formation of [3H]lyso-PAF from 1-[3H]alkyl-2-acyl-sn-glycero-3-phosphocholine. It appeared that a major function of albumin in the incubations was to complex the [3H]lyso-PAF formed, thus removing this end-product from the reaction.